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A DISCUSSION OF GRANITE: 


Its Essential Properties, Natural Classification, 
Uses, &c,, together with a Brief Discussion 
of the Distinctive Characteristics of some 


of the Leading Granites of the day. 


JOHN GLENVILLE MURPHY, E.M. 


(FORMERLY TERRITORIAL GEOLOGIST OF WYOMING). 





ALSO 


A REPORT ON THE GRANITE PROPERTY 


COLUMBIA GRANITE COMPANY. 


— BY — 
tRA HoH, WOOLSON, E.M. 


(OF THE ENGINEERING DEPARTMENT OF COLUMBIA 
COLLEGE, N.Y.) 





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GRANITE 
As a Stone in Building and Construction. 





Building-stone requires accurate obser- 
vation combined with practical experience 
in the field. A knowledge of the mineral con- 
stituents may be obtained from standard text- 
books, but nothing more. This will be clearly 
seen as we proceed with our subject. 
Building-stone must be studiedwith reference 
to its hardness, durability, beauty, chemical com- 
position, resistance to crushing force and struct- 
ure. It is evident that the durability of a stone 
does not depend on its hardness or the strength 
of a sample alone. Equally, if not more impor- 
tant in this respect, is the chemical composition. 
Each must be studied in its order, and we will 
confine ourselves to the granitic rocks. as their 
superiority over all other stone used in construc- 
tion is now recognized by architects, builders 
and engineers. 
In giving the strength of granite produced in 
the -principal quarries we shall quote from the 


elke ACQUIRE a thorough knowledge of 


3 


most reliable authorities. The durability and 
capability of resisting climatic influences depends 
primarily upon the chemical composition; but, as 
the granite from the principal quarries has not 
been studied with reference to this important 
factor, we can make no comparisons in this 
respect, 


GRANITE. 


Very few people can be found who are willing 
to confess ignorance with regard to what they 
deem so simple a rock as granite. The book 
student will say that it is a rock made up of the 
minerals quartz, feldspar and mica, and thinks 
he has exhausted the subject. The layman will 
say, ‘‘Why, it is the stone in such and such 
buildings, and in this and that wall,” and express 
surprise that so simple a question should be 
asked. As a matter of fact, the subject is ex- 
tremely difficult, and in the following discussion 
we will ask — first, the indulgence of the student, 
and second, his careful consideration of the facts 
herein presented. We have studied all the stand- 
ard works on the subject and find much con- 
fusion. 


CRYSTALLINE SILICIOUS ROCKS. 


Of this group we shall only consider granite, 
syenite and gneiss. In commonor quarry nomen- 
clature these rocks are termed granites, and in- 
deed it is often difficult to determine to which 


4 


class a particular rock belongs; and we may 
safely say that it is impossible to separate them 
in field practice if the definitions of the authorities 
are followed. 


‘Granite consists of quartz, feldspar and 
mica.” 
—DANA’sS MINERALOGY. 
‘*Syenite consists of quartz, feldspar and 
hornblende.” 
—DAna’s MINERALOGY. 
**Gneiss consists of quartz, feldspar and mica, 


possessing cleavage planes.” 
—DANA’s MINERALOGY. 


‘* Gneiss is a Stratified granite.” 


—Dr. HAwes, Report, Vol. 10, Tenth 
U.S. Census. 


He says: ‘‘ The gneisses or stratified granites 
are extensively quarried, and stratification is a 
circumstance very favorable to the extraction of 
the stone for some purposes. For example, the 
perfection of cleavage incertain directions makes 
it easy to split large slabs from the mass, to be 
used for curbing, paving, steps, etc. The stones 
can be split in such a way as always to possess 
two parallel flat surfaces—a circumstance which 
_ Simplifies the construction of walls from them. 
There are no uses to which granite can be ap- 
plied to which the gneis$oid rocks cannot also be 
applied, and some of the largest quarries in the 
United States, which are designated granite 
quarries, really produce gneiss.” 


—Vol. 10, Tenth U. S. Census. 
5 


We cannot say that the definitions of Dana 
are incorrect, inasmuch as these rocks contain 
all the minerals mentioned. It will be seen, 
however, that most granites contain other min- 
erals. The definition of gneiss can be called 
faulty, inasmuch as the physical difference be- 
tween gneiss and granite is not noted, and which 
is in reality the only difference between the two 
stones. 

The article of Dr. Hawes written for the 
tenth census is not merely faulty, but mislead- 
ing, and much mischief may result from it. The 
term ‘‘ stratification” is used for ‘‘ cleavage.” A 
moment’s thought will show this to be incorrect. 
Cleavage comprehends stratification, and much 
more; for example, crystals possess parallel 
cleavage on the crystalline planes, which cannot 
correctly be called stratification. Again, it 
seems to be implied that all granite which ex- 
hibits parallel cleavage is gneiss—we use the 
term ‘‘exhibits” in the sense that is evident on 
mere inspection, for all granite will be shown to 
possess parallel cleavage. 

This is a serious error; for all fine-grained 
granite has distinct cleavage planes, and the 
stone produced in some of our most famous 
granite quarries would be called gneiss. 

So important a matter as this requires careful 
consideration. To express the property which 
some rocks have of more readily splitting on one 
plane than on the other, four words are com- 
monly used as synonyms—viz., cleavage, stratifi- 
cation, rift and lamination. As applied to gran- 
ite, a moment’s thought will show any one that 

6 


the terms lamination and stratification are not at 
all applicable. The term rift, used by all quarry- 
men, is applicable to massive granular rocks, 
and signifies the plane of easiest cleavage—that 
is, facility to split in a particular direction. The 
term cleavage is equally proper, but more gen- 
eral in its application; so that the term rift, 
being specific for its particular purpose, will be 
adhered to. 

That all granites possess more or less rift is a 
well-known fact, and we hear the quarrymen 
speak of the stone from a particular quarry as 
having a good or bad rift. We never hear them 
speak of a granite in which the rift is entirely 
absent. The rift is a very important considera- 
tion to quarrymen, since to its greater or less 
perfection is due the ease with which a stone can 
be quarried or worked into forms. That all 
granites possess a rift is also well known to engi- 
neers and experimenters who test the stone for 
the purpose of determining its resistance to 
crushing force. They speak of the samples as 
being tested on bed or onedge. The so-called 
bedding in this case is coincident with the rift. 

Cleavage planes, or the rift in granite rock, 
results from two causes, viz.: Pressure, or the 
aggregation of a portion of the mica into parallel 
layers. 

‘A moment’s reflection will show that the first 
cause must be general, from which, as well as 
the experience of quarrymen, it results that all 
granites havea rift. 

The second cause is not general, from which 
it also results that there is a distinct physical 


7 


difference in granitic rocks. (We will return to 
this under the head of Gneiss.) 

The rift in true granite is caused solely by 
pressure, and its greater or less*perfection is 
governed by two causes, viz.: first, the amount of 
pressure to which it has been subjected during 
solidification ; and second, the size of the crystal- 
line particles of which the rock is composed. 
We may assume that the pressure sustained by 
granite forming the outer crust of the earth is 
practically the same for all sections, no matter 
how distant (since the pressure was that due to 
the superincumbent mass during solidification and 
the amount of erosion since that time necessarily 
very great), so that we need consider the size of 
the crystalline particles alone as affecting the rift. 
From this it results that the finer the crystalline 
particles the more perfect it is; and as the crys- 
talline particles increase in size, the more faintly 
evident it becomes, and finally, when the crystals 
become very large and the granite necessarily 
coarse, no rift is evident by mere inspection, 
though its existence and direction is well known 
to the quarrymen who work it. 


GNEISS.. 


Totally different from the foregoing are the 
cleavage planes or rift caused by the aggrega- 
tion of a part of the mica into parallel layers or | 
planes, which, in additien to causing the stone 
to split readily into slabs having flat parallel 
surfaces, also weakens it along the line of these 
planes, which is not the case with the cleavage 

8 


planes resulting from pressure. (See result of 
tests made by Mr. I. H. Woolson, of the En- 
gineering Department of Columbia College, 
New York, annexed to this report.) 

We may say, then, that gneiss consists of 
quartz, feldspar and mica, possessing parallel 
cleavage planes due to the aggregation of a 
portion of the mica into parallel layers. 

The physical difference just noted is alone 
what separates gneiss from granite. In distinct- 
ive types of each stone the difference is quite 
striking. 

We have found that there is merely a physical 
difference between granite and gneiss; from a 
mineralogical or chemical standpoint, they are 
the same. Granite and syenite are physically 
the same, while they differ simply in the fact that 
in syenite the mica is replaced by hornblende. 
As these two varieties of stone are the most im- 
portant rocks used in building and construction, 
we will consider them with care. 

Granite is defined as a rock consisting of 
quartz, feldspar and mica; syenite is a rock con- 
sisting of quartz, feldspar and hornblende. Be- 
tween these distinctive types we find nine-tenths 
of the commercial granites, and we hear such 
terms as hornblende granite, hornblende-mica 
granite, epidote granite, syenitic granite, gran- 
itie syenite, etc., etc. 

Commercially these rocks are the same, no 
matter whether they consist of quartz, feldspar 
and mica, quartz, feldspar and hornblende, 
quartz, feldspar and pyroxene, or a mixture of 
all these as well as other minerals. 


9 


Structurally the stones are the same, which 
perhaps accounts in a measure for the commercial 
acceptation. Naturally, where the eye alone is 
used for inspection, structure alone is regarded ; 
and we would ask if this is not the safest as well 
as the less embarrassing plan? If a chemical 
classification is attempted it results in confusion 
to the ordinary business man, who simply wishes 
to know that a good, durable stone is to be em- 
ployed. Tell him that he is to have a harnblende- 
biotite granite, which contains no pyroxene and 
but little pyrites, and in nine*cases out of ten we 
would be met with a look of amazement, and the 
answer that it was his business to pay for his 
structure when it was completed in accordance 
with the specifications, and our business to fur- 
nish acceptable material. 

What surprises us mostly is that all these so- 
called varieties are not comprehended under one 
name—viz., granite or syenite. Let us examine 
the question critically, and see if it would be war- 
ranted. A stone which tothe naked eye consists 
almost exclusively of quartz, feldspar and mica 
is called by the best writers typical granite ; but 
other writers introduce confusion even here by 

subdividing this, the simplest form, into several 
classes, according to the kind of mica. Thus, 
when the mica is a white muscovite, they give us 
a muscovite granite. When a dark biotite mica, 
a biotite granite, and when the stone contains a 
fair proportion of each, a muscovite-biotite gran- 
ite. Here is the first stumbling-block to the 
honest searcher aftertruth. He has under consid- 
eration several pieces of granite. One contains 


- 


Io 


quartz and feldspar, with the muscovite and 
biotite micas about equally distributed. Another 
contains the-same minerals, but about four times 
as much muscovite as biotite ; another about four 
times as much biotite as muscovite; another 
contains both micas, but a very small proportion 
of the biotite—yet enough to be distinctly visible, 
etc., etc. We would now ask the reader to clas- 
sify these granites if he wishes to do so. If we 
are asked to doso, we shall be pleased to answer, 
“This is a typical granite ’””—or, more broadly— 
‘This is granite.” ” 

A stone which consists almost exclusively of 
quartz, feldspar and hornblende is called in like 
manner by the best writers a typical syenite. 
(We will say here that the typical granites and 
syenites, so-called, are never found extensively 
in large quarry operations.) We rarely find 
a stone which contains an appreciable amount 
of hornblende without pyroxene. See Quincy, 
North Conway and Cape Ann granites. It is 
also rare to find extensive bodies—we doubt 
their existence at all--of granite without mica, 
so that again voluminous writers confuse us with 
such terms as syenitic granite, granitic syenite, 
hornblendic granite, hornblende-pyroxene gran- 
ite, pyroxenic syenite, micaceous syenite, horn- 
blende-biotite granite, etc., etc. What will our 
earnest searcher after truth do here? 

These minerals occur in granite or syenite, if 
the latter term is preferred, in very variable pro- 
portions. When there is visible to the naked 
eye four, six, eight or fifty times as much horn- 
blende as mica or pyroxene in the rock, what 


It 


shall we call it? We cannot call them impure 
granites or syenites, as this would imply imper- 
fection, notwithstanding that a stone which con- 
tains hornblende and mica may be an excellent 
granite. 

We have now reached the point at which we 
have been aiming—?. e., May not the scientific 
world with propriety adopt the same term as the 
commercial world for these different varieties of 
the same stone, and thus save endless confusion 
by reducing the subject to the simplicity which 
really belongs to it? We think so: let us see. 
Structurally all these varieties’ are undeniably the 
same—have they the same origin? We believe 
so, and that they form the great mass of the prim- 
itive rock. Many writers recognize—in their 
writings—metamorphic and vein granites. That 
granitic structure may have been produced on 
the small scale by metamorphic action and vein 
deposition may be admitted, but we doubt that 
any considerable body of granite has been so 
formed. We will return to this again. Let us 
pass through geologic time and conceive the con- 
dition of our globe when it was a liquid mass 
revolving in space, with our seas, lakes, rivers, 
etc., existing in the shape of steam and vapor in 
the outer chromosphere. Let us follow the 
gradual subtraction of heat and consequent 
gradual solidification of the earth’s crust, due to 
radiation. The same laws of force then as now 
governed the mass. That is to say, our orbit 
was the trajectory, resulting from an equilibrium 
between centrifugal and centripetal forces, and 
the law of gravity also was the same then as now. 


12 


Hence, we readily see that the heavier metals 
and compounds would be drawn toward the 
centre, the lighter materials forming the outer 
crust. Now, since the same forces were in opera- 
tion all over the earth’s crust, it results that sim- 
ilar effects were produced—that is to say, the 
crust all over the globe must have been similar ; 
but this crust constitutes the whole of the primi- 
tive rock, from which it results that the primitive 
rock must be similar structurally, though abso- 
lute chemical uniformity cannot. be expected, as 
will be shown. The slow cooling of the mass 
accounts for the crystalline structure ; but it may 
be asked, What evidence have we that the primi- 
tive rock is granite or syenite? We answer, that 
the great mass of the earth’s crust at this day is 
composed of granite and the minerals resulting 
from its disintegration. The great subdivisions 
of the rock constituting the earth’s crust are the 
primitive, sedimentary, volcanic, plutonic and 
chemical— with the plutonic we include the meta- 
morphic. 

After the solidification of the primitive crust 
and the continuous radiation of internal heat, 
moisture was deposited which would flow to the 
greatest depressions, producing disintegration 
and erosion of the crust already formed, which, 
being deposited by the waters and reconsolidated 
by pressure and heat, form the sedimentary rock. 
Metamorphic rock consists of these deposited 
sediments re-fused and crystallized, and some 
writers class as metamorphic such portions of 
the primitive rock as may also have been re- 
fused and crystallized, but the sedimentary and 


us 


metamorphic rock taken together consists of the 
elements of granite. 

Furthermore, the great mass of rock fronting 
our sea-shores is granite. In great mountain 
upheavals the peaks are invariably granite, be- 
cause even if originally sedimentary, the great 
denudation at the exposed peak in time reaches 
the granite ; there can be no question, then, that 
granite is the primitive rock. We have shown 
that all granites possess cleavage planes, or rift. 
That this must.be the fact seems evident ; for, 
since the formation of the crust great erosion has 
taken place, and is measured by the total sedi- 
mentary rock, part of the metamorphic plus the 
greater part of the gravels and sands; conse- 
quently, the granite exposed on the surface to- 
day existed at great depth at the time of its forma- 
tion, and was therefore exposed to great pressure 
from the superincumbent mass. This pressure 
must have interfered with the formation of per- 
fect crystals, and flattening took place on the 
points exposed to this pressure, resulting in cleav- 
age planes or rift, at right angles to the line of 
pressure, as announced in the first part of this 
article. 

It has been shown that, in accordance with 
the law of gravity, the lighter material of our 
globe should form the earth’s crust, or the primi- 
tive rock. That this is what has actually taken 
place is shown by the fact that, while the specific 
gravity of the whole earth is 5.5, that of the crust 
will not average more than 2.6; hence we should 
expect the primitive rock to be formed chiefly of 
silica and the silicates, quartz, feldspar, mica, 


14 


hornblende, pyroxene, epidote, garnet, tourma- 
line, chlorite, etc. 

By microscopic examination, no less than 
thirty different minerals have been found in 
granite—(see Vol. 10, Tenth U. S. Census)— 
which should teach us to avoid chemical classifi- 
cation. 

Now, while the magma composing the earth’s 
crust contained so many different minerals, is 
there anything which would lead us to believe 
that their distribution was uniform? It is even 
absurd to suppose that such would be the case. 
Even in blast-furnace practice, where the ore and 
flux are mixed with ail possible care, we never- 
theless find some slags acid and some basic. The 
idea that nature would produce an exact division 
and arrangement of the elements forming its 
magma over so enormous a space is not to be 
entertained. Hence we find similar structure 
but variable composition. The quantity of quartz 
and feldspar even is variable —(see analysis of 
granites in any of the standard authorities)—but 
this is not only true of granite from different 
quarries, but also of the stone in the same quarry. 
If we have shown that all granites and syenites 
are the same, not only structurally, but that they 
have the same origin, why not adopt a single 
name for all of them? Call the rock either gran- 
ité or syenite, and much confusion will be avoided 
thereby. 

We have stated that we doubt if any consider- 
able bodies of granite have been produced by 
metamorphic action or in vein filling. It is evi- 
dent at the outset that the erosion of the primitive 


bs) 


rock by the action of water must also have 
produced a sorting and rearrangement of the 
materials. Thus a stone which originally con- 
sisted of quartz, feldspar and mica, when disin- 
tegrated and the materials transported by water 
to considerable distances, would deposit the 
heavier and coarser material first, while the thin 
flakes of mica would be carried to much greater 
distances ; consequently, any metamorphic gran- 
ite must be such as has been re-fused and recon- 
solidated in place. The reader can decide if he 
thinks much of this has taken place, or whether it 
should be called metamorphic granite at all. We 
hardly think it worth while to discuss the possi- 
bility of the existence of any considerable bodies 
of vein granite ; a moment’s reflection will show 
the absurdity of such an idea. We will now 
proceed to a more particular discussion of 
granite. 


ESSENTIAL ELEMENTS OF GRANITE. 


We can with propriety divide the minerals of 
a granite into essential and accessory elements, 
the essential elements being those which are 
invariably present and form nearly the whole 
mass of the rock, while the accessory elements 
are those which exist in small or minute quantity 
and even in some quarries may be entirely absent. 

The essential elements are quartz, feldspar, 
mica and hornblende. (Pyroxene and epidote 
in some varieties of granite become essential 
elements by taking the place of the hornblende 

16 


or mica wholly or in part—see light green variety 
of North Conway granite and the deep green 
variety of the Adirondack Granite Company— 
this, however, is not of frequent occurrence). 
Among the most frequently occurring accessory 
elements are pyroxene, epidote, pyrites, chlorite, 
garnet, tourmaline, magnetite and the oxide 
of iron (rust), as a decomposition product. 
Granites are spoken of as being light gray, 
gray, dark gray, cream-colored, pink, red, green 
(as seen in some varieties of the Adirondack 
stone), and purple (Swedish granite). There are 
also gradations and blending of all the colors 
above mentioned. 

Let us consider the essential elements and 
the modifications of color produced by them, If 
the minerals were precisely the same in physical 
appearance, chemical constitution, and the crys- 
tals were of the same size, then granite would be 
invariable. Suchis not the case, however; the 
elements vary in color and in the size of the 
crystals, so that we find a striking difference in 
color and texture not only in granites’ quarried 
in different sections, but also in the same quarry. 
Pure quartz consists of silica (Si, O;), two chem- 
ical elements, silicon and oxygen. As it occurs 
in nature 999 parts in 1000 are not pure. The 
amount of impurity is variable in character and 
quantity, thus modifying its color and appear- 
ance. In color it passes through all gradations 
from white (milky quartz) to black (flint). Thus 
we have the quartz crystal, agate, carnelian, 
amethyst, etc. It is also transparent, translu- 
cent or opaque. 


7 


Feldspar is a complex silicate, consisting of 
the silicates of alumina, potash, soda and lime in 
varying proportions. (The chemical discussion 
of the elements would occupy too much space, 
and will be omitted for that reason). In color it 
is gray, yellow, pink or red. 

Mica is also a complex silicate; colors, white 
(muscovite), black (biotite). Hornblende, pyrox- 
ene and epidote are also complex silicates ; 
colors, white, passing to green and black. 

We see, therefore, that there is a most marked 
difference in the essential elements of granite, 
from which it results that it is very variable in 
color. Another modification results from the 
difference in the size of the crystalline particles, 
so that we recognize coarse and fine grained 
granite. The most important differences, how- 
ever, result from what are improperly called ac- 
cidental impurities, and which affect the value 
of the stone for all construction purposes. 


ACCESSORY ELEMENTS. 


The consideration of the accessory elements 
forms by far the most important factor in the in- 
vestigation of granite, of which no less than 
thirty have been found in the various samples 
submitted to microscopic examination and chem- 
ical analysis. We will only consider those 
which occur in appreciable proportions, and play 
an important part in the modification and value 
of the stone. Hornblende forms an essential 
element in many of the granites, but it also 

18 


occurs in many varieties in small proportion, 
and is then considered an accessory element. 
The others are pyroxene, epidote, chlorite, tour- 
maline, garnet, magnetic and titanic iron, iron 
pyrites and the oxide of iron, as a decomposition 
product resulting from the oxidation of the 
pyrites. 

Some of these elements, as hornblende, tour- 
maline and garnet, are not objectionable where 
strength alone is considered. Pyroxene, epi- 
dote, chlorite, titanic and magnetic iron are det- 
rimental to granite as accessory elements, but 
the pyrites is more detrimental than all the other 
elements combined, and is of far more frequent 
occurrence; in fact, a close inspection will show 
its existence in many of the so-called standard 
granites, which on exposure to atmospheric 
action produces an unsightly stain of iron rust 
(oxide of iron). 

This element is also damaging to the stone 
by aiding and, when in any considerable quan- 
tity, producing disintegration of the whole mass. 
It will then be seen how important is the chem- 
ical determination of the constituents of granite, 
and that hardness or resistance to crushing force 
alone is not sufficient to determine the relative 
value of granite; nor is it safe to accept stone 
from any quarry without an examination, for the 
quality of the stone varies even in the same 
quarry, and one contract might be filled with 
stone that would be entirely satisfactory, while 
the stone supplied for another would be much 
inferior. Many people will recommend and use 
stone from a particular quarry because stone 


19 


from that quarry has been used for a number of 
years and has given satisfaction. This they do 
on the erroneous assumption that the quarry will 
always produce stone of the same quality. The 
practice is not only dangerous but expensive, as 
many new quarries produce a superior stone 
and sell it cheaper. The only safe plan is to 
make an examination of the stone which it is 
proposed to furnish. 

We have said that stone should be studied 
with reference to its hardness, durability, beauty, 
chemical composition, resistance to crushing 
force and structure. Let us briefly consider 
these qualities. Hardness is very desirable, 
because it admits of working the stone, so that 
sharp, well-defined edges are produced. Itis 
not so readily scratched and defaced, and is one 
of the requisites of durability. The durability of 
a stone depends on its hardness, resistance to 
crushing force and chemical composition. Ifa 
stone contains an element which is soluble in 
atmospheric waters, then it is unfit for building 
purposes. Also if a stone contains a mineral 
which is soluble in acid waters, it is unfit for use 
as a building stone in manufacturing centres. 
None of the essential elements of granite are 
soluble in any of these waters; but when it con- 
tains pyrites as an accessory element, then it 
contains a material which by change becomes 
soluble. The first change which it undergoes on 
exposure to atmospheric action is oxidation, by 
which the sub-oxide of iron and some sulphate 
of iron are formed. At this stage both are solu- 
ble in water and are washed out. The next stage 


20 


is per-oxidation, by which an insoluble oxide of 
iron(rust)is formed. The effect of these changes 
is seen in buildings constructed of stone which 
contains even a small percentage of the pyrites. 
The sub-oxide of iron is formed, which being 
soluble, is washed out of its place by rain-water, 
and which, spreading over the face of the stone, 
becomes partly per-oxidized, forming unstghtly 
stains of iron-rust;.this effect is seen in any 
building constructed of stone which originally 
contained this mineral. Its occurrence in build- 
ing-stone is more frequent than is generally 
supposed. 

The beauty of a stone depends upon its 
purity, freedom from undesirable accessory ele- 
ments, hardness which gives it form, and struct- 
ure. The question of color is a matter of taste. 
The stone should be free from pyrites, pyroxene, 
epidote, etc. It should be regular in structure, 
that is, the quartz and feldspar should not occur 
in bunches or aggregations (termed ‘‘ white 
horse” by the quarrymen). The mica also when 
in bunches detracts from the beauty of a granite. 
For general use a fine grained stone is much 
hanasomer and stronger than a coarse grained 
one, except perhaps for use in large columns, 
where the coarseness of the crystals will not ap- 
pear to such disadvantage. The importance of 
the chemical composition, resistance to crushing 
force and structure have been considered and 
discussed in the preceding part of this article. 

The characteristics of the granite from some 
of the most important quarries in point of public 
favor might be noted. 


The Quincy granite contains both hornblende 
and mica, but the former in much the greater 
proportion. It isa coarse-grained stone, quite 
dark when polished, and mottled in appearance, 
because of the large amount of hornblende, and 
also that some of the quartz is transparent. It 
contains some pyroxene, which is brittle and 
friable, as can be seen in the numerous holes in 
a hammered face. It also contains iron pyrites 
in appreciable proportion, as can be seen in old 
monuments and in buildings where the stone has 
been exposed to atmospheric action for five or 
six years. 

The granite quarried at Cape Ann (at Rock- 
port and Lanesville) contains both hornblende 
and pyroxene and but little mica. The chief in- 
dustry is the manufacture of paving stones and 
coarse ashlar, because the stone contains more - 
iron as an accessory element than the Quincy, 
which, as shown, is detrimental for fine work. 
It is also a coarse-grained stone. 

The North Conway, N.H., granite is coarse- 
grained ; colors, red and green. The red is the 
principal variety; it contains both hornblende 
and pyroxene, no mica. The green variety con- 
tains epidote and chlorite, in addition to the 
hornblende and pyroxene. This variety is used 
chiefly for paving. The railroad depot at Port- 
land, Me., is constructed of the red stone, and 
notwithstanding its coarseness, looks well, as it 
is used in large blocks and columns. 

The Maine granites in general are coarse- 
grained, the exceptions being the Hallowell and 
Friendship stones. The latter stone contains 


22 


enough pyrites in the samples we have seen to 
be extremely detrimental. (See the arch at the 
entrance to Prospect Park, Brooklyn, N.Y.) 

The Hallowell stone deserves particular at- 
tention, as it has attained a high rank in public 
favor. It is fine-grained and comparatively pure; 
color, gray; mineral constituents, quartz, feld- 
spar and mica, mainly- the white muscovite 
variety of this mineral. The feldspar is the 
white albite or soda spar; quartz, opaque. It is 
a good stone, but by no means what we would 
consider a high class granite, though it is exten- 
sively used for statuary. The stone is readily 
worked and the rift is plainly evident. 

The granite quarried at Concord, N. H., is 
. known as silver granite, which name is due to 
the fact that fhe stone contains an excess of white 
muscovite mica, which occurs in flakes possess- 
ing in this form a silver lustre. It is fine- 
grained; color, gray; rift, evident. This stone 
has received much favor for some purposes. 
Constituents, opaque quartz, soda feldspar and 
white muscovite mica. 

The granite quarried at Millstone Point, near 
Niantic, Conn., would be a strictly first-class 
stone were it not that it contains considerable 
pyrites. It is fine and close-grained in texture. 
Constituents: Quartz (opaque to translucent), feld- 
spar (part sodaand part potash spar), mica (mostly 
biotite with some hornblende in fine, needle-like 
crystals). The stone is massive; rift not dis- 
tinctly visible by inspection. 

The granite which was formerly quarried at 
Groton, Conn., was very similar to Millstone rock. 


23 


The most famous quarry operated up to this 
date is known as the Smith Quarry, located near 
Westerly, R. I. Structurally it resembles the 
stone of Millstone Point and Groton, Conn., but 
in color it is slightly different, being what quarry- 
men would call richer. In a rough sample the 
difference in color is not so evident, but in pol- 
ished samples it is quite distinct—the Millstone 
ona polished surface showing dark gray, while 
the Westerly has a distinct tint of brown. This 
difference is due to the fact that the Westerly 
contains more potash feldspar. Minerals same 
as Millstone. 

In conclusion we would say that architects, 
engineers and builders have not always the 
requisite facilities for determining the value of a 
material for use in construction, but they can 
always have it done without much expense. The 
resistance to crushing strain can be determined 
at the establishment of the Messrs. Fairbanks & 
Co., or more accurately, at the School of Mines, 
Columbia Coliege, and the U. S. Arsenal at 
Watertown, Mass. The resistance to crushing 
force which any stone should stand will in most 
cases be estimated by the use to which it is put. 
Thus the strongest stone should be selected when 
it is to be used in a position that will be subjected 
to great pressure. 

When it is proposed to use a stone for exterior 
work, its adaptability to the atmospheric con- 
ditions should be noted. Thus, any building- 
stone containing limestone as an ingredient 
should not be employed when it is to be sub- 
jected to acid conditions of the atmosphere, as at 


24 


as 


Pittsburgh, Penn., Trenton and Newark, N. J. 
etc., or any large manufacturing centre, as de- 
facement and disintegration of the stone will be 
rapid. 

Any material adapted for exterior construc- 
tion should be free from pyrites. The existence 
of this mineral will not weaken the stone in a 
fresh sample, nor is its existence in small quan- 
tity readily detected, except by chemical analysis. 
A very small quantity is exceedingly detrimental 
to any stone which is destined for building or 
ornamentation. 


GRANITE THE STONE OF THE 
FUTURE. 


There are no uses for any stone used in con- 
struction to which granite cannot be applied. 
When pure and fine-grained it offers great resist- 
ance to crushing force, and is not disintegrated 
by any atmospheric conditions. Itiswelladapted 


“to ornamentation as it takes a high polish, and 


also finishes under the hammer and chisel to 
sharp and regular edges. It can be worked into 
any forms to which even marble is susceptible. 
The light gray varieties of granite produce by 
far the most beautiful statuary; though more 
expensive to produce fine work from it on the 
start, it more than compensates this drawback by 
being practically indestructible when produced. 


JOHN GLENVILLE Murpnuy, E. M. 


25 


Part I1.-A New Granite. 


The granite to which we especially wish to 
call attention was recently discovered near the 
Narrows of the Connecticut River, four miles 
southeast of the city of Middletown, Conn. It 
occurs on a high bluff fronting the river on the 
west shore, and is described in the accompanying 
report of I. H. Woolson, E. M., of the Engi- 
neering Department of the School of Mines of 
Columbia College. This report speaks for itself. 
With regard to the tests, we may say that they 
ase the most thorough and extensive series of 
tests ever made upon stone from a single quarry, 
and forcorroborative evidence we sent four cubes 
to be submitted to a compressive strain at the 
Government Hydraulic Testing Machine at the 
U.S. Arsenal, Watertown, Mass. The remark- 
able resistance is given herewith, and fully con- 
firms the results obtained by Mr. Woolson. The 
owners of the property, now the Columbia Gran- 
ite Company, desired to have an exhaustive 
examination of the stone made for their own 
knowledge, and also to satisfy the public that the 
granite was of exceptionally high quality in all 
respects. Their most sanguine expectations have 
been more than realized. 


NEw York City, 
July rith, 1892. 
COLUMBIA GRANITE COMPANY, 
MIDDLETOWN, CONN. 
GENTLEMEN—I have lately visited your gran- 
ite property at Middletown, as you requested, 
26 


x 


and carefully examined the various ledges ex- 
posed. I have also made an exhaustive series of 
tests upon the crushing strength of samples 
taken from the different out-crops, and respect- 
fully submit the following report: 

The property is located on the Connecticut 
River, four miles below Middletown, and is one 
of the most delightful spots along the shores of 
that beautiful river. The property contains fully 
a thousand acres, and the supply of granite on 
the same is ‘practically inexhaustible. The 
ledges are numerous and prominent; they stand 
out boldly from the surrounding soil, and present 
the finest opportunities for quarrying purposes. 
They run continuously across the property, nearly 
parallel with the river, for a distance of over two 
miles, and in many places they project forty to 
fifty feet above the surface, thus exposing hun- 
dreds of thousands of tons ready for excavation 
without any ‘‘ stripping” whatever. The ship- 
ping facilities are of the best. With a railroad 
directly through the property, and two and one- 
half miles of river front, it is difficult to see how 
they could be much improved. 

There seems to be no doubt that the property 
is capable of being developed into one of the 
largest and finest granite quarries in the country. 
The quality of the stone is excellent, as is con- 
clusively shown by the accompanying report of 
tests. It is of two varieties and in amount about 
equally divided betweenthem. One is a coarse- 
grained granite of reddish cast, due to the flesh- 
colored feldspar, and contains a moderate amount 
of fine black mica. It is susceptible of gocd 


a7, 


polish, and will make a beautiful and effective 
stone for architectural purposes, while its great 
strength will adapt it for use in piers, founda- 
tions of large buildings, arches or any place 
where it will be subjected to heavy crushing 
strain. 

The other variety is a very fine-grained, light 
gray stone of exceeding beauty and strength. 
Its crystalline structure is particularly compact 
and uniform. It breaks with a clean, sharp 
fracture, the surfaces of which are almost glassy 
in appearance. It possesses a most extraordi- 
nary toughness and resistance to crushing force, 
which qualities render it particularly desirable 
for use in places where it will be subjected to 
excessive wear and shock, as in paving, curbing 
and the like. It takes an elegant polish, and 
this fact, together with its fine grain and uniform 
structure, admirably adapts it for monumental 
purposes or ornamental use of any kind where 
chiseled surfaces are required. Neither of the 
varieties show any trace of iron, which is decid- 
edly in its favor, for many otherwise good gran- 
ites are ruined for building purposes by the 
presence of this impurity. 

In the question of strength this stone is quite 
phenomenal. From the following tabulation of 
results and the report of tests, it will be seen 
that a series of nine (9) tests which I made upon 
2-inch cubes of the coarse-grained stone from the 
‘‘N.W. end of Ledge” gave an average of 
23,000 lbs. per sq. inch, and a similar series of 
seven (7) tests made upon samples taken from 
the ‘‘ Middle Ledge,” gave an average of 22,000 

28 


Ibs. per sq. inch, or an average of 22,500 lbs. for 
the sixteen (16) specimens, thus demonstrating 
the extreme uniformity in quality, for these 
samples were taken from places distant from 
each other fully 4000 feet. 





Nine (9) SAMPLES FROM SEVEN (7) SAMPLES FROM 
‘““N.W. END OF LEDGE.” ‘* MippLE LEDGE.” 
Lbs. per sq. inch. Lbs. per sq. inch. 
Pa.00). =. bed. 21,460 - Bed. 
21,450 - Edge. BE QOD els eas 
2E019 = vy 24,753 - pA 
24,278 - 4; 21,921.- = 2 
22,525 - Bed. 22,197 - Edge. 
22,475 - a 21 831 - fi 
23,525 - ee 20,470 - 4 
25,450 - Edge. 
23,542 - Bed. 
207,264 9 —23,029 155, 290-7 =22,184 
23,029 
22,184 





45,213 —2—22,600 


This average of 22,600 lbs. per sq. inch for 
the whole of the red variety is.exceedingly high, 
but even this is small when compared with the 
results obtained from the gray granite. 


On this latter variety I made tests upon twelve 
(12) cubes cut from samples taken from different 
parts of the ledge. 


29 


The average of the whole gave the extraor- 
dinary result of 31,600 lbs. per sq. inch, while 
one specimen stood 34,000 lbs. per sq. inch. 


TWELVE SAMPLES OF FINE-GRAINED GRAY 
GRANITE, 


Lbs. per sq. 7n. 
8205 4. eds 
$1,019... >, =a 
82.700). 35): ee 
30,050... SS eas 
32 000) Js eke sue Reels 
82,562... - {ines 
30:000° 
29,4005," <)> >) alee 
34,0754. = ee 
39 0507, "<i y-) Neca 
NOR ie Mea ce oe 
32,150. oe ete Beas 





379,919 12—31,659. 


The very unusual character of these figures 
will at once become manifest by comparing them 
with the results obtained by similar tests made 
upon the various famous granites of the world. 

The best Scotch granites are diversely quoted 
by different authorities at 8,000 to 14,000 lbs. per 
square inch. In this country such authorities as 
Professors Baker, Thurston and Gen. Gillmore 
give the strength of the best granites as ranging 
from 10,000 to 20,000 lbs. per square inch. Gen. 
Gillmore made a very elaborate series of tests 


39° 


upon building stones for the U. S. Government, 
and his results are usually taken as the authority. 
He made a hundred tests in duplicate upon the 
different granites of the country, and out of the 
whole list his maximum test was 22,000 lbs. per 
square inch, and only three chance cubes from 
different localities scored this figure. One-half 
of the whole lot were crushed with a load of 
15,000 lbs. per square inch or less, and the large 
majority of the other half failed under 19,000 lbs. 
Gillmore includes in his table three other speci- 
mens which stood a little over 22,000 lbs., but 
they came from Staten Island and New Jersey, 
and it has been proven they were trap and not 
granites, so they cannot be considered. The 
same general average runs through the results, 
of which I have a large number, obtained by dif- 
ferent experimenters, such as Prof. Newberry, 
the Engineer of the Brooklyn Bridge, and others. 

It is rare indeed to find a granite which is 
recorded as standing’ more than 18,000 lbs. per 
square inch ;—22,500 lbs. is the maximum result 
recorded by any expert upon any granite so far 
as I know, and in my own experience I have only 
found one variety which has surpassed that 
figure. 

A comparison of this data with the results 
obtained from your stone is very remarkable, for 
the whole series of sixteen (16) tests upon the 
coarse-grained samples gave me an average of 
22,500 Ibs.; a similar average of the twelve (12) 
tests upon the fine-grained variety gave 31,600 lbs., 
which is 10,000 lbs. more per square inch for 
every specimen crushed than Gillmore obtained 


31 


from the three best samples out of a hundred. 
These figures are significant, and show conclu- 
sively the exceptional strength and toughness of 
your stone. 

An inspection of the Report of Tests shows 
another peculiar feature-—-namely, that both vari- 
eties are equally as strong crushed upon the edge 
as upon the bed face. Stone is usually supposed 
to bear much greater compression on its natural 
bed than if its laminz are at right angles to the 
bed joints. In your stone it seems to make no 
difference. 

This characteristic may be quite useful and 
economical in working the fine-grained stone, for 
its uniform structure makes it equally as attract- 
ive to the eye whichever way it is laid. 

All these facts afford conclusive evidence of 
the superiority of your stone, and prove that it is 
eminently suited for all uses where a high-grade 
granite is desired. 


Very respectfully yours, 


IRA HARVEY WOOLSON, E. M. 















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